Field of Invention
Various embodiments of the present invention relate to a method and an apparatus for synchronizing a physical layer link channel.
Description of Related Art
Recently, DOCSIS 3.1 (data over cable service interface specifications 3.1) standard for data transmission up to 10 Gbps through cable networks has been under development. The DOCSIS 3.1 has attracted attention for having key technology which enables existing cable networks to transmit data up to 10 Gbps without an optical cable.
The DOCSIS 3.1 is different from the conventional version of DOCSIS in light of a channel error correction method and a modulation method. The DOCSIS 3.1 adopts an OFDM method (orthogonal frequency division multiplexing) which is a multi-carrier transmission method, thereby improving spectral efficiency more than 50% by applying downlink maximum 4096 QAM and uplink maximum 1024 QAM for each sub-carrier. The multi-carrier system using the OFDM may perform symbol synchronization and channel equalization with comparative ease in comparison with a single carrier, and have the advantage of using a portion of a plurality of sub-carriers constituting a frequency band for transmission and reception control.
In DOCSIS 3.1, the frequency band for transmission of upstream and downstream transmission has been extended for broadband channel transmission and transmission up to 10 Gbps. Since the extended frequency band corresponds to a range in which a conventional single carrier channel is available, it becomes impossible to receive the channel only by frequency tuning in the DOCSIS 3.1.
Thus, the DOCSIS 3.1 may provide a sub-channel in a particular structure in a broadband channel for receiving downlink wide-area channel. The above is referred to as PLC (physical layer link channel). The PLC may be allocated to a portion of sub-carriers used for control among a plurality of sub-carriers constituting the frequency band. The PLC may transmit is a time stamp for system operation of a receiver, power management information, downlink channel operational profile definition information and multi-carrier channel information, the number of sub-carriers used to create an OFDM code from a transmitter, a location of the sub-carrier of a pilot used for timing synchronization and the channel equalization, and modulation parameter, for example, a coding rate of a channel correction encoder. Accordingly, the receiver may gain information regarding entire channels and system information by acquiring a PLC channel prior to receiving entire band, and demodulate and decode the OFDM code receive by using acquired information.
To this end, the receiver should perform PLC synchronization in order to receive the PLC properly.